1. Field of the invention
The present invention relates to an apparatus for forming flat-bottomed plastic bags, and to a method of forming such bags. More particularly, the present invention relates to a method of, and an apparatus for forming flat-bottomed plastic bags having precision formed gussets in the sides thereof, which gussets are formed subsequent to the initial manufacture of the hollow tubing which is the starting material for the bags. In a preferred embodiment, microperforations are formed in a portion of the bags to allow ventilation thereof The present invention further relates to a finished bag, which is produced using the method and apparatus of the invention.
2. Description of the Background Art
Some types of foldable flat-bottomed plastic bags are available on the market today, and different methods are used for their manufacture. One type of plastic bag forming machine and method of operation is disclosed in U.S. Pat. No. 4,929,224 to Hanson et al., which uses closed sleeve plastic material with inwardly gusseted sides as a raw starting material. Another method of making flat-bottomed plastic bags is disclosed in U.S. Pat. No. 5,102,384 to Ross et al., the disclosure of which is incorporated by reference herein, insofar as it is not inconsistent with the present disclosure.
FIGS. 1 through 1C of the drawings, provided herewith, illustrate a part of the known method of forming flat-bottomed plastic bags from a roll of pre-gusseted or pleated tubing. In the method of Ross et al, a portion of a pre-gusseted plastic film tube is unrolled from a roll of such tubing stock, and the tube is cut and sealed at a bottom section thereof to define a bag 10. Then, an upper surface 12 of the bag 10 is grasped by a movable upper vacuum clamp 14, a lower surface 16 of the bag 10 is grasped by a fixed lower vacuum clamp 18, and the upper and lower surfaces are moved apart. Subsequently, the movable upper clamp moves toward the top of the bag while holding a transverse section thereof, to fold a rectangular shape into the bottom of the bag, and creases are made in the corner edges of the bag 10 to form a flat bottom therein.
Unfortunately, it has been found that the commercially available pre-gusseted tubing is not made with the pleats or gussets formed at a consistent depth from the outside edge of the tubing, but rather, contains gussets in which the depth varies to an excessive and unacceptable degree. Moreover, other variations may exist in the pre-gusseted tubing which can also lead to problems.
Referring now to FIG. 1B, it may be seen that in properly shaped pre-gusseted tubing, evenly-shaped gussets 20, 22 are formed in the sides of a portion of tubing so that upper and lower gusset legs 24, 26, respectively, are of the same length. Accordingly, when vacuum, symbolized by the arrows in FIG. 1B, is applied to the upper and lower clamps 14, 18, transversely along the upper surface of the tube, the upper surface 12 is picked up by the upper clamp 14, and the lower surface 16 is held by the lower clamp 18.
In contrast, however, when the pre-gusseted tubing is not made properly, as shown in FIG. 1C, it may have gusset legs 24c, 26c, of different lengths, so that one leg 24c may extend beyond another 26c. As a result, when vacuum is applied to the upper and lower clamps 14c, 18c in this instance, point B on the upper leg 24c has vacuum applied from both above and below. Therefore, the material at point B may not be pulled into the proper clamp. It is unpredictable which direction the material at point B will go, and therefore, a proper bag may not be formed.
Therefore, a need exists in the art for a more consistent and precise method and apparatus for forming flat-bottomed plastic bags.
In addition, some problems exist when attempting to pack hot food such as, e.g., hamburgers, into a plastic bag, because condensation caused by steam from the food tends to form inside the bag, which may be detrimental to the food in the bag. A plastic bag with an ability to `breathe` might be helpful to solve this problem.
Accordingly, it is an object of the present invention to provide a method and apparatus for forming flat-bottomed plastic bags which gives more consistent and precise results than are obtainable using pre-gusseted tubing. It is another object of the present invention to provide a method and apparatus for forming flat-bottomed plastic bags which involves forming gussets in tubing which initially does not have any pleats or gussets previously formed therein.
It is another object of the present invention to provide a method and apparatus for forming flat-bottomed plastic bags that are permeable to moisture, and to provide such moisture-permeable bags as a product thereof
Other objects, features and advantages of the present invention will become apparent from a review of the following detailed description section, which should be read in conjunction with the drawings.